Detect which systemd cgroup mode is used

[wentasah]

The modes are described here. Currently, we hardcode support only for the hybrid mode.

From the above linked document:

If you wonder how to detect which of these three modes is currently used, use
statfs() on /sys/fs/cgroup/. If it reports CGROUP2_SUPER_MAGIC in its
.f_type field, then you are in unified mode. If it reports TMPFS_MAGIC then
you are either in legacy or hybrid mode. To distinguish these two cases, run
statfs() again on /sys/fs/cgroup/unified/. If that succeeds and reports
CGROUP2_SUPER_MAGIC you are in hybrid mode, otherwise not.
From a shell, you can use check the Type in stat -f /sys/fs/cgroup and
stat -f /sys/fs/cgroup/unified.